The present invention generally relates to an intramedullary system for coupling bone portions across a fracture therebetween and, more specifically, to an intramedullary hip pinning system for rigidly interconnecting a femoral head portion to the remaining portion(s) of the femur and across a fracture or fractures in the area of the femoral neck or the shaft of the femur or combinations of such fractures.
Bones are the hard parts of the skeleton found in vertebrates. In its most basic construct, bones are formed of a relatively soft, spongy cancellous material surrounded by a much harder cortex. The cancellous bone yields under relatively low loading, while the much more dense cortical bone supports much higher loading.
A hip joint is a heavily stressed, load-carrying bone joint in the human body. It is essentially a ball and socket joint formed by the top of the femur which rotates within a cup-shaped aceta bulum at the base of the pelvis. When a break or fracture occurs adjacent to the top of the femur, the separated portions of the femur must be held together while healing occurs.
Historically, there have been a number of techniques used for treatment of fractures of the proximal end of the femur. In early parts of this century, patients were merely placed in bed or in traction for prolonged periods, frequently resulting in deformity or death.
In the 1930s, the Smith-Peterson nail was introduced. This device was inserted into the intramedullary canal of the femur resulting in immediate fixation of hip fractures, early mobilization of the patient, and a lower morbidity and mortality. A number of nails have been introduced for fracture fixation of the femur in its proximal end, including the Jewett Nail and Enders Nail.
Intramedullary nails have been inserted down the entire length of the femoral canal to provide a basis for the fixation. Threaded wires, standard bone screws or cannulated bone screws were then inserted through or along side the proximal nail and into the femoral head to provide fixation and rotational stability. The conventional nails did not provide compression of the proximal bone fragments against each other. Also, in longer nails the distal tip of the nail tended to rotate out of plane which forced the surgeon to locate the distal screw holes using fluoroscopy by a method commonly known as xe2x80x9cfree-handingxe2x80x9d.
In the 1960s, the compression hip screw was introduced, resulting in improved fixation of the proximal femur. A lag screw assembly was inserted into the femoral head, a plate was attached to the lateral femur, and a compression screw joined the two. These implants provided a more rigid structure for the patient and allowed the surgeon to compress the fractured fragments against each other thereby decreasing the time to mobility. A number of compression hip screws have been introduced for fracture fixation about the proximal femur, including the Dynamic Hip Screw.
During implantation these compression hip screws require an incision at least equal to the length of the plate being used which extends operative time and blood loss. The side plate also creates a protuberance on the lateral side which provides an annoyance to the patient. Compression hip screw systems also fail to provide adequate compression in oseteogenic patients because the lag screw assembly threads fail to obtain sufficient purchase due to poor bone stock. Poor purchase is known to contribute to nonunion, malunion and the lag screw assembly eroding through the superior bone of the head of the femur in a condition known as xe2x80x9ccut outxe2x80x9d. Additionally, many patients are dissatisfied with the results of compression hip screw surgery because of the excessive sliding to a medial displacement and shortening position which leads to a change in gait.
Newer devices and inventions include additions to the nail and lag screw assembly to ease or eliminate the need to locate the distal screw holes and improve the fixation. These newer devices are commonly classified as xe2x80x9cexpanding devicesxe2x80x9d and expand in size after placement to fill the intramedullary cavity. Freedland, U.S. Pat. Nos. 4,632,101, 4,862,883 and 4,721,103, Chemello, U.S. Pat. No. 6,077,264 and Davis, U.S. Pat. No. 5,057,103 describe a method of fixation which provides points which contact the internal cortical wall. In these patents a mechanism is actuated deploying arms or anchor blades through the cancellous bone to contact the inner cortical wall. These methods are complex and difficult to retract should the nail or lag screw assembly require extraction. Further, the screws do not deploy through the cortical bone.
Other expanding devices provide surface contact with the intemal cortical wall resulting in a wedge effect. Kurth, U.S. Pat. No. 4,590,930, Raftopoulos, U.S. Pat. No. 4,453,539 and Aginski, U.S. Pat. No. 4,236,512, among others have described mechanisms which deploy or expand with a molly bolt concept. These methods are complex and difficult to retract should the nail or lag screw assembly require extraction and, also, do not deploy through the cortical bone.
Bolesky, U.S. Pat. No. 4,275,717 was the first to discuss engagement within the cortical wall. However, Bolesky""s invention does not address controlled penetration into the wall and required permanent implantation of the actuation rod. In addition, Bolesky does not address the fundamental problem of the actuation rod""s protrusion extramedullarly into the surrounding musculature.
In U.S. Pat. Nos. 5,976,139 and 6,183,474B1, Bramlet et al describe a surgical anchor which has deployable tangs. These tangs are simple in design, internally positioned, yet easily deployed into, and if desired through, the cortical bone providing improved purchase for compression of a fracture, especially in osteogenic bone. These tangs are just as easily retracted should the device require explantation.
Approximately 10 years ago Howmedica (Rutherford, N.J., United States) was the first to produce the xe2x80x9cGamma Nailxe2x80x9d, named for its similarity in shape to the Greek letter, and other designs soon followed. These devices combined desirable aspects of both intramedullary nails and compression hip screws. These intramedullary hip compression screws required a few small incisions, allowed capture of the most proximal fragments of the femur, rigid fixation of the most proximal and distal fragments, and a sliding lag screw assembly or anchor which fits within a barreled sleeve for allowing improved compression of the fragments as the patient ambulates and begins to bear weight on the fractured limb. The nails are typically held in place on the distal end through interference forces with the intramedullary canal and through the use of locking screws.
The Gamma Nail""s shape accommodates the relative shape of the greater trochanter and femoral neck and head fragments, and the shape of the hip is therefore preserved. Nonunions are less frequent because bone-to-bone contact is maintained and the bulk of an intramedullary hip screw blocks excessive sliding. Intramedullary hip screws work best in reverse obliquity fractures, a fracture, in which compression hip screws are least effective.
Osteogenic bone still provides a poor medium for purchase of the lag screw assembly of the Gamma Nail inhibiting adequate compression and rotational stability. Longer nails continue to see the distal tip of the nail rotating out of plane forcing the surgeon tolocate the distal screw holes by the free-hand method. The free-handing technique leads to an increased surgical time and exposes the surgeon and patient to increased radiation dosages.
Clearly a need exists for a system which is superior to the, xe2x80x9cgold standard,xe2x80x9d of compression hip screws while minimizing the surgical insult to the human body. Such a system, as disclosed and claimed herein, includes a simple, effective and controllable fixation device which allows greater purchase of the lag screw assembly within the femoral head, improved compression across the fracture line, provides a means of rotational stability both in the femoral head and in the femoral shaft, and minimizes the need for additional distal incisions to locate and place locking screws. This system allows the surgeon a choice of penetration distance within the femoral head and femoral shaft fixation based upon the injuries presented and the desired level of treatment. Finally, this system allows explantation to occur as easily as implantation.
An intramedullary nail system is provided for coupling bone portions on opposite sides of a fracture. The intramedullary nail system according to the invention is especially suitable for installation within the medullary canal of a fractured long bone, such as found in an arm or leg. In one embodiment of the present invention, the intramedullary nail system includes an elongated rod with radial portals which allow passage of locking screws or anchoring tangs and a lag screw assembly. The rod has a distal end and a proximal end with internal threads. A lag screw assembly having an externally threaded portions. The radial portals in the distal end allow passage of internally deployable and retractable anchoring tangs or cortical screws. A radial portal in the proximal end accommodates a sleeve which passes through the intramedullary nail and through which the lag screw assembly passes freely while preventing rotation of said lag screw assembly. A compression screw engages the sleeve and cooperates with the internal threads of the lag screw assembly trailing end providing axial translation of the lag screw assembly within the sleeve. The proximal end has an axial portal for an end cap with external threads on the trailing end which engages the internal threads of the intramedullary nail. The end cap has a parabaloid leading end which engages the sleeve thereby preventing translation and rotation of said sleeve.
When the intramedullary nail is placed into position the anchoring tang assembly is actuated to deploy the tangs out from their stowed position into the cortical bone. The tangs are deployed to any desired position thereby achieving a desired fixation based upon the quality of the bone.
In one embodiment, cortical screws may be placed to secure the intramedullary nail with the surrounding cortical bone. In another embodiment, the tang assembly is actuated and the tangs are deployed to any desired position thereby achieving the desired fixation based upon the quality of the bone.
The sleeve is coaxially inserted over the lag screw assembly""s trailing end and through the intramedullary nail. An end cap is threaded into the intramedullary nail with it""s leading end contacting and frictionally holding the sleeve. By providing interference against the sleeve, the sleeve is prevented from altering its position either through translation or rotation.
The compression screw passes through the sleeve and engages the lag screw assembly. As the compression screw is tightened the lag screw assembly and associated first bone portion are pulled against the intramedullary nail and second bone portion resulting in compressive forces being applied across the fracture.
The intramedullary nail is preferably cannulated to allow passage of one or more anchoring tang assemblies. These anchoring tang assemblies are inserted from the proximal end towards the distal end and the tangs deployed by means of an actuator driver. An alternate embodiment describes a retracted anchoring tang assembly which is permanently placed within the distal end of the intramedullary nail and is deployed or retracted by means of an actuator driver from the proximal end of the intramedullary nail.
The lag screw assembly preferably contains a permanently placed anchoring tang assembly stored in a retracted position within the leading end. The tangs are deployed or retracted from the trailing end of the lag screw assembly.
The anchoring tang assembly contains arcurate shaped tangs that are permanently attached to the assembly""s main body. These tangs are initially formed into a prescribed position for storage. As the assembly is actuated, and the tangs deploy, the tangs are formed into their final shape through interaction with the portal of either the intramedullary nail or the lag screw assembly.
The compression screw preferably contains a patch of ultra-high molecular weight poly-ethylene (UHMWPE) within the threads. This provides constant positive engagement between the compression screw external threads and the lag screw assembly internal threads.
The end cap preferably contains a patch of ultra-high molecular weight poly-ethylene (UHMWPE) within the threads. This provides constant positive engagement between the end cap external threads and the intramedullary nail internal threads. In its final position the end cap exerts a force upon the sleeve which inhibits the sleeve from sliding or rotating out of a prescribed position.
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.